I have never voted in a Presidential election on one issue alone, but I will this year.

We all know there are crucial economic and social issues. If you are out of a job, what could be more pressing? There are foreign policy challenges with Russia, China, North Korea and the Middle East. I do not mean to minimize the urgency of these issues. But this year, for me, they must all take a back seat.

Although I recently delivered the benediction at the Democratic National Convention, I considered the act religious, not political — a blessing, not an endorsement. My decision this year will be simple: I will vote for whichever candidate seems likelier to stop Iran from obtaining a nuclear weapon.

There are two words that symbolize the terror of the twentieth century: Auschwitz and Hiroshima. An Iranian bomb threatens to combine them both. It portends the destruction of an entire nation and an entire people in a moment. However hard it may be to imagine such wholesale slaughter, if history has taught us nothing else, it has taught that today’s delusions of madmen can become tomorrow’s reality.

The problem is not one person. True, Iranian President Mahmoud Ahmadinejad describes Israel as an “insult to humanity” and “a cancerous tumor,” and calls for its “disappearance.” But it is equally true that in May, the chief of staff of the Iranian armed forces, Major-General Seyed Hassan Firouzabadi, said: “The Iranian nation is standing for its cause [and] that is the full annihilation of Israel.” And in June, Iranian Vice-President Mohammad Reza Rahimi told a United Nations-sponsored anti-drug conference that the Jews were responsible for the spread of illegal drugs around the world, that the Zionists control the international drug trade, and that they had ordered doctors to kill black babies.

Experts from Israel’s former Mossad Chief Meir Dagan and others point to a genuine concern that Iran would bomb Israel. So those like The New York Times‘ Bill Keller who declare that Iran would not use the bomb are foisting their own humanitarian criteria on people who do not share them. The reasoning seems to be: “Since for me it is unthinkable, it must be impossible.” But we have learned to our cost in the twentieth century, when it comes to atrocity, the unthinkable is indeed possible. “Containing” a nuclear Iran is the opposite of real politik; it is fantasy politik.

After all, even if we stipulate for a moment that Iran would not bomb Israel, the problem is hardly solved. Would they give nuclear weapons to proxies in Hezbollah? Of course not, right? Who would trust Hezbollah with a nuclear weapon? But we have seen in Pakistan that a single brilliant, unscrupulous man can change the nuclear balance. And even if the regime were itself restrained, and exercised an improbable degree of discipline, what would its nervous neighbors do? Saudi Arabia is not likely to stand idly by while its neighbor attains instant hegemony. They know with whom they are dealing, even if we sometimes forget: After all, the long, savage Iran–Iraq war was fought largely by children given a “token” to ensure their entrance to heaven should they be martyred. That is not a mentality designed to encourage confidence in international restraint and wisdom.

This week was Rosh Hashana, the day in the Jewish tradition that the world was created. Another sacred scripture, the Bhagavad Gita, went through the mind of Robert Oppenheimer as he saw the first atom bomb explode near Los Alamos: “Now, I am become Death, the destroyer of worlds.”

With the exception of Hiroshima and Nagasaki, humanity has managed to restrain itself from deploying this most awful of weapons, the one that can indeed destroy worlds. We stand before an iron law of history: you cannot unmake what has been made. Once Iran has a nuclear bomb, the world will never look the same. Not only Israelis, but the West will never sleep easily in its bed. Stopping Iran will not feed your family, get you a job or open a factory. It will not elevate the level of public discourse or bring manufacturing back from China. It will merely ensure that the free world, beginning with Israel but not ending there, will not live under the shadow of annihilation. To our presidential candidates: show me you have a way to do that, and you’ve got my vote.